OBJECTIVE: To perform preclinical studies to examine neural circuits and mechanisms underlying primate sleep. RESULTS Increased daytime emotionality, anxiety, and depression are commonly associated with sleep alterations. Since the amygdala plays an important role in emotional processing and is connected to sleep regulating regions, we are in the process of examining the role of the primate amygdala in regulating sleep. These studies are of particular relevance since sleep patterns in rhesus monkeys are similar to those in humans. Using highly selective techniques, ibotenic acid lesions of the amygdala were performed in 17 rhesus monkeys. The effects of these lesions on frontal EEG asymmetric activity and sleep are currently being studied. All regional EEG data have been collected and are awaiting analysis. Sleep studies have been completed in 4 lesioned and 2 control animals. Overall, the data demonstrate that chair adapted rhesus monkeys exhibit relatively normal patterns of sleep as defined by stages 1-4 and REM. Preliminary data suggests that amygdala lesioned animals may be engaging in sleep associated with less awakenings and longer REM periods. Heart rate data has also been collected and will be of interest since autonomic instability occurs during REM. FUTURE DIRECTIONS Another 12 animals will be studied this year to more completely characterize the role of the amygdala. In addition, histological analysis will be performed on the brains of these animals to correlate sleep changes with site and extent of the lesion. KEY WORDS emotion, anxiety, sleep, REM, amygdala, lesion and Department of Psychiatry